Igneous Rock (Volcanic Glass)

Agate

Silicon dioxide (chalcedony, SiO2)

Basalt with Amygdules

Extrusive mafic igneous rock

Basalt (Water-worn)

Aphanitic Mafic Igneous Rock

Likely reddish granite/porphyritic igneous rock fragments

Feldspar–quartz–mica aggregate, possibly pink granite or rhyolite

Likely polished rhyolite or porphyritic volcanic rock

Rhyolite, possibly flow-banded or altered rhyolite; composition mainly quartz and alkali feldspar with minor biotite/iron oxides

Porphyritic Basalt

Extrusive Igneous Rock

Kimberlite

Ultramafic igneous rock

Weathered porphyritic volcanic rock, possibly rhyolite or andesite

Altered porphyritic rhyolite–andesite; likely quartz/feldspar phenocrysts in a fine volcanic groundmass

Pumice or Vesicular Basalt/Scoria (water-worn)

Vesicular volcanic rock

Weathered basalt cobble

Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, with possible olivine and iron oxides

Weathered basalt cobble

Basalt; fine-grained mafic volcanic rock, mainly plagioclase and pyroxene with possible olivine and iron oxides

Likely basalt

Basalt; predominantly plagioclase feldspar, pyroxene, and commonly olivine

Vesicular basalt (probable)

Basalt; chiefly plagioclase feldspar, clinopyroxene, and iron-rich minerals, with vesicles possibly lined by zeolites or calcite

Agate Geode

Silicon Dioxide (SiO2) - Chalcedony variety

Porphyritic volcanic rock, likely andesite or basalt with weathered feldspar phenocrysts

Porphyritic andesite–basalt; chiefly plagioclase feldspar and pyroxene, with possible olivine or iron oxides

Basalt

Extrusive Igneous Rock

Rhyolite (likely porphyritic)

Rhyolite; chiefly quartz, alkali feldspar, plagioclase, and volcanic glass, with possible iron-oxide staining

Weathered vesicular volcanic rock, likely pumice or scoria

Vesicular rhyolitic pumice or basaltic scoria; exact identification requires a clearer image and tests

Iron-rich volcanic rock, possibly hematite-bearing basalt

Basalt with iron oxides/hydroxides, chiefly hematite (Fe₂O₃) and possibly magnetite (Fe₃O₄)

Basalt Pebble

Extrusive Igneous Rock

Possibly black obsidian or polished basalt

Volcanic glass (obsidian; chiefly SiO₂) or fine-grained basalt

Pumice

Extrusive volcanic rock (Vesicular Rhyolite/Dacite/Andesite)

Scoria (vesicular volcanic rock)

Basaltic or andesitic scoria; chiefly plagioclase, pyroxene, and iron-rich volcanic glass

Vesicular Basalt (Lava Rock)

Vesicular Basalt

Weathered basalt pebble

Basalt, a fine-grained mafic volcanic rock; likely olivine- and pyroxene-bearing

Scoria (vesicular volcanic rock)

Basaltic scoria; chiefly plagioclase, pyroxene, olivine, and volcanic glass

Basalt

Extrusive Igneous Rock

Rhyolite

Extrusive felsic igneous rock

Basalt

Extrusive igneous rock

Weathered volcanic breccia (possible basaltic-andesite breccia)

Volcanic breccia: angular to subrounded volcanic clasts in a finer volcanic matrix; exact composition cannot be confirmed from the photograph

Dacite / Andesite Tuff

Intermediate Volcanic / Pyroclastic Rock

Agate

Silicon dioxide (SiO2)

Likely granite or granitic rock fragment

Granite (inferred; exact identification is uncertain from the blurred image)

Basalt

Extrusive igneous rock

Basalt Pebble

Extrusive mafic igneous rock

Porphyritic Igneous Rock / Rhyolite Porphyry

Porphyritic volcanic rock

Vesicular basalt (possibly scoria)

Basalt; chiefly plagioclase feldspar, pyroxene, and often olivine, with volcanic glass

Basalt (River Pebble)

Extrusive Mafic Igneous Rock

Basalt (River Pebble)

Extrusive mafic igneous rock

Basalt (River Pebble)

Extrusive mafic igneous rock

Basalt

Basalt (Mafic igneous rock)

Basalt with Quartz Vein

Extrusive Igneous Rock with SiO2 Vein